Intra-arterial chemotherapy offers an alternative to systemic (iv) chemotherapy for localized neoplasms. Infusion of chemotherapeutic agents directly into the arterial supply of the neoplasm allows, under proper circumstances, higher local tissue concentrations without a corresponding increase in systemic toxicity. Results using this treatment method in patients have varied. In some instances, cases of severe ophthalmic toxicity and of leukoencephalopathies have been reported. These findings suggested the possibility that streaming of the infused drug solution resulted in inadequate mixing and therefore non-uniform drug concentrations in the infused tissue region. Fluid-mechanical studies with an in vitro model of a human carotid artery system have demonstrated that streaming can occur at low infusion rates, and that mixing can be enhanced by increasing the infusion velocities and also by improving the design of the catheter tip, such as injecting transversely or retrograde to the artery flow. In vivo studies involving both slow and fast infusions of radiolabeled iodoantipyrine into the carotid artery of monkeys and subsequent autoradiographic analysis of brain slices have corroborated the findings of the in vitro model studies.